1. Technical Field of the Invention
The present invention relates generally to wireless communication systems and, more particularly, to a unified technique of processing dedicated pilot segments of STTD and CLTD signals in diversity mode with a pilot segment in non-diversity mode for a downlink receiver in such a wireless communication system.
2. Description of Related Art
Mobile communication has changed the way people communicate and mobile phones have been transformed from a luxury item to an essential part of every day life. The use of mobile phones today is generally dictated by social situations, rather than being hampered by location or technology. While voice connections fulfill the basic need to communicate, and mobile voice connections continue to filter even further into the fabric of every day life, the mobile Internet is the next step in the mobile communication revolution. The mobile Internet is poised to become a common source of everyday information, and easy, versatile mobile access to this data will be taken for granted.
Third generation (3G) cellular networks have been specifically designed to fulfill these future demands of the mobile Internet. As these services grow in popularity and usage, factors such as cost efficient optimization of network capacity and quality of service (QoS) will become even more essential to cellular operators than it is today. These factors may be achieved with careful network planning and operation, improvements in transmission methods, and advances in receiver techniques. To this end, carriers want technologies that will allow them to increase downlink throughput and, in turn, offer advanced QoS capabilities and speeds that rival those delivered by cable modem and/or DSL service providers. In this regard, networks based on Wideband Code Division Multiple Access (WCDMA) technology may make the delivery of data to end users a more feasible option for today's wireless carriers.
The General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE) technologies may be utilized for enhancing the data throughput of present second generation (2G) systems such as GSM. The Global System for Mobile telecommunications (GSM) technology may support data rates of up to 14.4 kilobits per second (Kbps), while the GPRS technology may support data rates of up to 115 Kbps by allowing up to 8 data time slots per time division multiple access (TDMA) frame. The GSM technology, by contrast, may allow one data time slot per TDMA frame. The EDGE technology may support data rates of up to 384 Kbps. The EDGE technology may utilizes 8 phase shift keying (8-PSK) modulation for providing higher data rates than those that may be achieved by GPRS technology. The GPRS and EDGE technologies may be referred to as “2.5G” technologies.
The Universal Mobile Telecommunications System (UMTS) technology with theoretical data rates as high as 2 Mbps, is an adaptation of the WCDMA 3G system by GSM. One reason for the high data rates that may be achieved by UMTS technology stems from the 5 MHz WCDMA channel bandwidths versus the 200 KHz GSM channel bandwidths. With WCDMA, a number of new, communication channels are specified under the 3GPP telecommunication standard. For example, one of the channels that is utilized for establishing a radio link (RL) between User Equipment (UE) and a base station is a physical channel, such as the Dedicated Physical Channel (DPCH). DPCH conveys both data and control components in the downlink communication. The control part, also known as DPCCH, carries the dedicated pilot bits, transmit power control (TPC) bits and Transport format combination indicator (TFCI) bits. The data part, also known as the DPDCH, carries transport channel data.
For the dedicated pilot bits carried by the DPCH or DPCCH, they usually contain a known signal, such as a known sequence of bits, to aid the downlink receiver perform functions, such as channel estimation, noise power determination, signal power determination and/or signal-to-noise ratio determination. Other functions may be performed as well. A dedicated pilot that is included in a dedicated channel performs some or all of those functions in relation to the dedicated channel.
Dedicated pilot processing from a single transmitting antenna is generally known. However, as wireless communications attempt to improve signal transmission, many systems are now employing multiple antenna transmissions, which technique is commonly referred to as transmit diversity. One technique used in transmit diversity is Space Time Transmit Diversity (STTD). Another technique used in transmit diversity is Closed Loop Transmit Diversity (CLTD). A dedicated channel being transmitted in the transmit diversity mode may convey the same data, but the transmissions from the two antennas carry a different pilot signal. Because it is advantageous for a downlink receiver to have the ability to receive in any one of the potential transmitting modes, such a receiver in the UE would need to process the pilots in the various modes. For example, if a communication system is to allow for single antenna transmission, STTD transmission, CLTD transmission, or a combination thereof, a given receiver would need processing capability to operate in more than one mode. For the two transmit diversity modes, pilot patterns used on the two antennas in the DPCCH are chosen to be orthogonal. One undesirable consequence of this is in terms of SNR estimation. Although it works well for STTD in terms of SNR estimation, for CLTD the SNR estimated off the pilot bits does not truly reflect the SNR experienced by the data, if the same processing is to be followed as for STTD, in order to take advantage of the orthogonal pilot pattern. On the other hand, separate pilot processing circuitry and/or processing routines would typically increase the complexity of the UE. However, if a technique is develop to use the same circuitry and processing to accommodate the different modes of transmission while producing desired results for each transmit diversity mode, redundant circuitry/processes may not be needed and performance may be improved.
Accordingly, it would be advantageous to implement a unified processing technique to receive the different modes of transmission in a downlink receiver.